In fruit distilleries, there are basically two types of distillation devices:
Traditionally, fruit brandies are produced by double distillation on simple distillation devices without amplification. The distillation devices consist of the still with heater, the helmet, the spirit tube, the cooler and the template. In the first distillation, the so-called robbery distillation, all the alcohol is distilled off the mash. Several robber barrels are collected and subjected to a second distillation, the fine distillation, where the alcohol is further intensified and purified, with separation of the pre and post flows.
Modern distillation devices, on the other hand, are equipped with a booster, which makes it possible to produce flawless and intensified fruit brandies in a single distillation. Booster distillers consist of the still with heater, the booster (bottom and dephlegmator), possibly the catalyst, the spirit tube, the cooler and the receiver. Size and construction of the components were subject to strict legal regulations in Germany (distillery ordinance §116,4). In German compensation distilleries, for example, the useful volume of the still was prescribed: For new distilleries it was 150 l. For distillation devices approved before 1936, a useful volume of 300 l was still permissible. In addition, only boosters with a maximum of three bottoms and an attached dephlegmator were allowed to be used (Brennereiverordnung §116,4a).
Since January 1, 2018, the Alcohol Act and the Alcohol Tax Ordinance have been in effect. The volume of the still and the number of amplifier bottoms are no longer limited. Due to its good thermal conductivity and catalytic properties, copper is the material of choice for the still and booster plates. Ghost pipe, cooler and receiver should be made of stainless steel to avoid metal clouding and discoloration in the distillate.
Distilling pot with heating
In the past, the distillation devices were very simple. The copper bladder was used to amplify the steam and was transformed into a helmet. It was directly fired with wood. To operate such a device requires a lot of dexterity, because the mash burns easily and thus unpleasant, burnt substances are transferred into the distillate.
Nowadays, the still is heated indirectly by means of a water bath or steam. This allows fine control and the risk of overheating the mash with the associated distillate errors is much lower. By installing an agitator, the mash is evenly distributed and heated. This is especially useful when processing viscous pome fruit mashes. In any case, the water bath must be equipped with a pressure relief valve and a water level indicator. Between the bubble and the intensifier bottoms, an over-foaming bottom with a mash return pipe is normally installed to prevent high foaming mash particles from penetrating the intensifier bottoms.
Bubble plates are usually installed for reinforcement. Usually one bell per plate is used, but plates with several small bells are also produced to ensure an even more intensive mass and heat exchange between the vapor and liquid phases. The same objective is achieved by folds on the edges of the bell or a slightly different design of the distillation tray in the form of an arrangement of small rows of holes with a roof, which ensures fine atomization and a small particle size.
Each of these constructions is suitable for the distillation of a fruit mash, if it is guaranteed that an intensive mass and heat exchange between vapor and liquid phase is possible. This can be checked during distillation through the sight glasses, which are placed above each bottom. Ideally, an intensive “bubbling” can be seen over the entire surface of the bottom. With bell bottoms, it is important to ensure that the edge of the bell extends far into the liquid standing on the bottom. Only in this way will the bell force the rising vapour to flow through the liquid on the floor.
In modern distillation devices it is possible to switch off the effect of individual bottoms by opening a valve to drain the bottom and raising the bell. It makes sense to install a cleaning system to automatically clean the plates, dephlegmator and catalyst between distillations.
The term dephlegmator is derived from phlegm, the condensate of a heavy boiling liquid that precipitates and returns to the system. This means that a separating effect of the alcohol-water mixture does not take place by evaporation of the lower boiling liquid – as realized on the amplifier bottoms – but that the condensation of the heavier boiling liquids leads to an enrichment of the lower boiling components.
The reinforcing effect of the dephlegmator (or reflux condenser) depends on
– from its heat exchange surface
– the cooling water flow
– the temperature difference between cooling water and alcohol-rich steam.
The size of the heat exchange surface depends on the design of the dephlegmator. There are two basic types:
In the water box dephlegmator, only a cylindrical, closed metal vessel with a cooling water inlet and outlet is embedded in the upper part of the amplifier. Since the heat exchange surface is relatively small, the reinforcing effect is also relatively weak.
Greater enrichment is possible with the tube dephlegmator, in which numerous tubes pass through a cylindrical vessel through which cooling water flows. If the dephlegmator is too warm, especially at the beginning of the distillation, this weakens its reinforcing effect. Flow and overflow can no longer be separated cleanly from the middle run. Therefore, when carrying out several successive firings, make sure that the dephlegmator is cooled down before the next firing.
It has been recognized that the ethyl carbamate content of fruit brandies can be reduced by adding a catalyst. For this purpose, the copper surface of the distillation device is greatly increased. When the vapors come into contact with copper, hydrocyanic acid, a precursor of ethyl carbamate, reacts to form heavy copper compounds that cannot be transferred to the distillate.
The catalysts available today are installed in the distillation device between the dephlegmator and the cooler, either vertically on the column or laterally adjacent or horizontal. The copper catalysts can consist of packings, rings or lamellas. Regardless of the design, the catalyst can be switched off during distillation. Regular cleaning is important for the effectiveness of the catalyst, as the hydrocyanic acid and other mash ingredients react with the copper and form deposits. Fats and waxes also deposit on the surface of the catalyst and form water-repellent coatings. The result is that the prussic acid can no longer react with the copper and the catalyst no longer has any effect. For this reason, the catalyst should be rinsed with hot water between firings and carefully cleaned regularly with cleaning lyes and citric acid so that the copper surface becomes bright again.
Product cooler and template
From the ghost pipe the alcoholic vapors enter the product cooler. Today, tubular coolers made of stainless steel are almost exclusively used for this purpose. The cooling is done in countercurrent, so that the cold cooling water and the cold distillate meet each other only shortly before they are placed in front of each other. A temperature sensor is installed at the head of the cooler, which ensures that the cooling water is switched on or regulated via a controllable valve. The valve opens automatically as soon as hot steam reaches the sensor.
The distillate flows from the cooler directly into a receiver. This is a stainless steel vessel for collecting and draining the condensate. It is constructed in such a way that an alcohol meter floating inside it indicates the alcohol content of the distillate leaving the condenser during distillation. Thus, the template provides valuable information about the course of the distillation and the separation of the pre, middle and post flow.
In order to monitor the distillation process, temperature sensors can be installed at various points in the distillation device. It makes sense to monitor the mash temperature in the still and to measure the temperature of the distillate above the individual bottoms. In any case, the water temperature of the dephlegmator – preferably at the cooling water outlet – should be constantly monitored.
Under no circumstances should the thermometer in the ghost tube be missing, which provides clear information about the time of the necessary after-run separation. By sensory analysis in connection with observation of the thermometer at the spirit tube, an exact separation temperature can be determined for after-runs of this plant. In practice, this thermometer is connected to a horn which, when a specified temperature is reached, calls the distiller to separate the overflow.